Mesothelial Cells Participate in Endometriosis Fibrogenesis Through Platelet-Induced Mesothelial-Mesenchymal Transition

CONTEXT

While fibrosis in endometriosis has recently loomed prominently, the sources of myofibroblasts, the principal effector cell in fibrotic diseases, remain largely obscure. Mesothelial cells (MCs) can be converted into myofibroblasts through mesothelial-mesenchymal transition (MMT) in many fibrotic diseases and adhesion.

OBJECTIVE

To evaluate whether MCs contribute to the progression and fibrogenesis in endometriosis through MMT.

SETTING, DESIGN, PATIENTS, INTERVENTION, AND MAIN OUTCOME MEASURES

Dual immunofluorescence staining and immunohistochemistry using antibodies against calretinin, Wilms' tumor-1 (WT-1), and α-smooth muscle actin (α-SMA) were performed on lesion samples from 30 patients each with ovarian endometrioma (OE) and deep endometriosis (DE), and 30 normal endometrial (NE) tissue samples. Human pleural and peritoneal MCs were co-cultured with activated platelets or control medium with and without neutralization of transforming growth factor β1 (TGF-β1) and/or platelet-derived growth factor receptor (PDGFR) and their morphology, proliferation, and expression levels of genes and proteins known to be involved in MMT were evaluated, along with their migratory and invasive propensity, contractility, and collagen production.

RESULTS

The number of calretinin/WT-1 and α-SMA dual-positive fibroblasts in OE/DE lesions was significantly higher than NE samples. The extent of lesional fibrosis correlated positively with the lesional α-SMA staining levels. Human MCs co-cultured with activated platelets acquire a morphology suggestive of MMT, concomitant with increased proliferation, loss of calretinin expression, and marked increase in expression of mesenchymal markers. These changes coincided with functional differentiation as reflected by increased migratory and invasive capacity, contractility, and collagen production. Neutralization of TGF-β1 and PDGFR signaling abolished platelet-induced MMT in MCs.

CONCLUSIONS

MCs contribute to lesional progression and fibrosis through platelet-induced MMT.

Role of Versican in the Pathogenesis of Peritoneal Endometriosis

CONTEXT

Sampson's theory cannot explain why only some cycling women develop peritoneal endometriosis. Few studies have focused on the pelvic peritoneum, which receives regurgitated endometrial tissues. We hypothesized that molecular alterations in the peritoneum are involved in the development of peritoneal endometriosis and conducted a microarray analysis to compare macroscopically normal peritoneum sampled from women with peritoneal endometriosis (endometriotic peritoneum) and those without (non-endometriotic peritoneum). Versican, a major proteoglycan component of the extracellular matrix, is one of the molecules up-regulated in endometriotic peritoneum.

OBJECTIVE

To investigate the role of versican in peritoneal endometriosis. Design, Patients, and Main Outcome Measure: Endometriotic peritoneum and non-endometriotic peritoneum were subjected to RT-PCR, immunostaining, and Western blotting. The versican V1 isoform was stably transfected into Chinese hamster ovary cells (CHO-V1), and the effects of CHO-V1-derived conditioned medium (V1-CM) on primary human endometrial stromal cells were investigated with attachment, invasion, and proliferation assays. The effects of peritoneal fluid collected from endometriotic women (endometriotic PF) or cytokines/growth factors, which were shown to be elevated in endometriotic PF, on versican expression in a human peritoneal cell line (HMrSV5) were also examined.

RESULTS

Versican V1 expression levels were significantly higher in endometriotic peritoneum. In vitro, V1-CM promoted attachment to the HMrSV5 cell monolayer as well as the Matrigel invasion of endometrial stromal cells. Although versican V1 expression was up-regulated by TGF-β1 in HMrSV5 cells, it remained unchanged in endometriotic PF.

CONCLUSIONS

Our results suggest the involvement of peritoneal versican in the development of peritoneal endometriosis.

A fibronectin mimetic motif improves integrin mediated cell biding to recombinant spider silk matrices

The cell binding motif RGD is the most widely used peptide to improve cell binding properties of various biomaterials, including recombinant spider silk. In this paper we use genetic engineering to further enhance the cell supportive capacity of spider silk by presenting the RGD motif as a turn loop, similar to the one found in fibronectin (FN), but in the silk stabilized by cysteines, and therefore denoted FNCC. Human primary cells cultured on FNCC-silk showed increased attachment, spreading, stress fiber formation and focal adhesions, not only compared to RGD-silk, but also to silk fused with linear controls of the RGD containing motif from fibronectin. Cell binding to FNCC-silk was shown to involve the α5β1 integrin, and to support proliferation and migration of keratinocytes. The FNCC-silk protein allowed efficient assembly, and could even be transformed into free standing films, on which keratinocytes could readily form a monolayer culture. The results hold promise for future applications within tissue engineering.

Reviews: in vitro models to study the pathogenesis of endometriosis

Several in vitro models that attempt to replicate the intraperitoneal environment have been developed to study the pathogenesis of endometriosis. The chicken chorioallantotic membrane has been used, but it has not been well characterized and may introduce some species specific variables. In vitro models using human tissues include amniotic membrane, human peritoneal explants, and cell culture monolayers. These models have been used to qualitatively, quantitatively, and temporally assess attachment of endometrial cells to peritoneal mesothelial and subsequent transmesothelial invasion. These models have also been used to assess the role of cytokines in the development of the early endometriotic lesion. Two- and three dimensional invasion chamber models have been utilized to assess endometrial cell interactions with peritoneal mesothelial cells and the extracellular matrix. Invasion models are also useful to evaluate novel therapeutic approaches. This review will focus on the above models to assist reproductive scientists interested in the pathogenesis of endometriosis.

A novel in vitro model of the early endometriotic lesion demonstrates that attachment of endometrial cells to mesothelial cells is dependent on the source of endometrial cells

OBJECTIVE

To characterize the source of variability in endometrial stromal cell (ESC) binding to peritoneal mesothelial cells (PMC).

DESIGN

In vitro study.

SETTING

University medical center.

PATIENT(S)

Reproductive-age women without endometriosis undergoing surgery for benign conditions.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Binding of ESCs (n = 9) to PMCs collected from the anterior abdominal wall (AAW) (n = 5), a commercially available mesothelial cell line (LP9) (three different passages) and normal ovarian surface epithelium (NOSE) (n = 5).

RESULT(S)

There were no differences in the binding of same-source ESCs to mesothelial cells obtained from the AAW of different women, to different passages of LP9s or to NOSE of different women. There was a trend toward increased binding of ESCs to NOSE compared to AAW PMCs. In contrast, there were significant differences in the ability of ESCs obtained from different women to bind to same-source PMCs.

CONCLUSION(S)

There is significant variability in ESC binding to PMCs. This variation is dependent primarily on the source of the ESCs. The ESC binding to LP9 PMCs was similar to AAW PMCs and NOSE.

Different effects of amino acid-based and glucose-based dialysate from peritoneal dialysis patients on mesothelial cell ultrastructure and function

BACKGROUND

Peritoneal dialysis fluid (PDF) containing amino acids has been introduced recently aiming to improve the nutritional status of PD patients. Dextrose-based PDFs have been implicated in progressive functional and structural deterioration of the peritoneal membrane. Limited data are currently available regarding the effect of amino acid-based PDF on the function and ultrastructure of human peritoneal mesothelial cells (HPMCs), which play a critical role in peritoneal membrane pathophysiology.

METHODS

We investigated the effects of two commercially available PDFs, which utilized dextrose (1.5% Dianeal) or amino acids (1.1% Nutrineal) as the osmotic agent, obtained from patients after a 4 h dwell, on HPMC proliferation (MTT assay and cell counting) and viability [lactate dehydrogenase (LDH)release], interleukin-6 (IL-6) secretion (commercial enzyme-linked immunosorbent assay) and ultrastructure (scanning and transmission electron microscopy).

RESULTS

Exposure of HPMCs to 1.5% Dianeal reduced cell proliferation, total cellular protein synthesis, IL-6 secretion and cell attachment, but prolonged the cell doubling time on recovery, and increased LDH release (P<0.001, P<0.001, P<0.0001, P<0.0001, P<0.001 and P<0.001, respectively). The 1.1% Nutrineal reduced HPMC proliferation (P<0.001) and increased IL-6 secretion (P<0.0001), but did not affect cell attachment, LDH release, protein synthesis or cell doubling time. Ultrastructural studies of HPMCs exposed to Dianeal showed cell flattening, increased cell surface area, reduced microvilli, and intracellular organelles compatible with dysfunctional mitochondria. In contrast, the ultrastructural morphology of HPMCs was relatively preserved after incubation with Nutrineal.

CONCLUSIONS

Our results showed that HPMC ultrastructure, viability and protein synthesis were better preserved with amino acid-based PDF, compared with conventional dextrose-based PDF. The significance of IL-6 induction by Nutrineal remains to be elucidated.

The role of cytokines in endometriosis

PROBLEM

To review the literature on the role of peritoneal cytokines in the pathogenesis and endometriosis-related infertility.

METHODS OF STUDY

A MEDLINE search was conducted by the key words of cytokine and endometriosis in the English publications, and references identified within the identified papers were also reviewed.

RESULTS

Several cytokines including interleukin (IL)-1, 6, 8, 10, tumor necrosis factor (TNF)-alpha, and vascular endothelial growth factor (VEGF) were reported to be increased in the peritoneal fluid (PF) of women with endometriosis. Those cytokines may be involved in macrophage activation, inflammatory change and enhanced angiogenesis. However, some cytokines were less expressed such as IL-2, and interferon (IFN)-gamma. They reflect the impaired T- and natural killer (NK)-cell function. Endometriotic implants produce some factors, e.g. matrix metalloproteinases (MMPs), Bcl-2, and affect their capacity to implant into the peritoneum.

CONCLUSION

Peritoneal cytokines, which are produced by mesothelial cells, leukocytes and ectopic endometrial cells, interwork locally and systemically in women with endometriosis. More studies about the specific role and interactions of these cytokines are needed to improve the understanding of endometriosis and to develop novel therapies.

Adhesion of endometrial cells labeled with 111Indium-tropolonate to peritoneum: a novel in vitro model to study endometriosis

OBJECTIVE

To evaluate, in a new original in vitro assay, putative factors that could modulate the adhesion of endometrial cells to peritoneum.

DESIGN

Prospective, controlled in vitro study.

SETTING

Academic research laboratory.

PATIENT(S)

Fourteen nonmenopausal women undergoing hysterectomy or laparoscopy for benign gynecologic indication.

INTERVENTION(S)

Endometrial cells obtained from women with regular cycles without endometriosis were labeled with 111Indium and confronted in vitro with mouse peritoneum in the presence of various cytokines and/or antiadhesive compounds.

MAIN OUTCOME MEASURE(S)

Radioactivity in 111Indium-labeled endometrial cells.

RESULT(S)

The adhesion of human endometrial cells to mouse peritoneum was increased by treatment with pro-inflammatory cytokines (interleukin IL-1beta, IL-6, TNF alpha, TGF-beta1). Whereas heparan sulfate had no effect on cell adhesion, a gel of ferric hyaluronate (Intergel) was able to counteract the pro-adhesive effect of cytokines. Interestingly, the pretreatment of peritoneum with cytokines, 24 hours before cell seeding in the presence of the ferric hyaluronate gel, restored the cytokine-promoting effect on cell adhesion.

CONCLUSION(S)

Proinflammatory cytokines promote the in vitro peritoneal adhesion of endometrial cells. An antiadhesive hyaluronate gel used in clinics decreases the adhesion in a dose-dependent manner and reduces cytokine bioavailability.

Time series analysis of transmesothelial invasion by endometrial stromal and epithelial cells using three-dimensional confocal microscopy

OBJECTIVE

To evaluate endometrial adhesion and invasion of peritoneal mesothelium.

DESIGN

Descriptive study using confocal laser-scanning microscopy.

SETTING

University-based laboratory.

PATIENT(S)

Women undergoing surgery for benign conditions.

INTERVENTION(S)

Fluorescence-labeled peritoneal mesothelial cells (PMCs) were grown on coverslips. Fluorescence-labeled endometrial stromal cells (ESCs) and epithelial cells (EECs) and myometrial cells (Myos) were plated on the PMCs. Cultures were examined at 1, 6, 12, and 24-27 hours with differential interference contrast and confocal laser-scanning microscopy.

MAIN OUTCOME MEASURE(S)

Demonstration of adherence and invasion of endometrial cells through peritoneal mesothelium.

RESULT(S)

At 1 hour, there was adherence of the ESCs, EECs, and Myos on the perimeter of PMCs. There was no invasion by the Myos. By 6 hours, ESCs and EECs spread over the surface of the PMCs and extended cell processes through PMC junctions. Extension of pseudopodia under the PMCs followed. By 12 hours, there was vacuolization and lifting of PMCs that had been undermined by endometrial cells.

CONCLUSION(S)

This is the first time-phase study to demonstrate adherence and the process of invasion of endometrial cells through the mesothelium. The application of three-dimensional confocal laser-scanning microscopy is a novel technique that can be used to further examine mechanisms involved in the pathogenesis of the early endometriotic lesion.

Culture of menstrual endometrium with peritoneal explants and mesothelial monolayers confirms attachment to intact mesothelial cells

BACKGROUND

To evaluate adhesion of menstrual endometrium (ME) to intact peritoneal mesothelium.

METHODS

Explants of peritoneum were cultured for 1 h with ME (n = 6). Specimens were serially sectioned for haematoxylin and eosin stain and immunohistochemistry using an anti-cytokeratin antibody to label mesothelium. Confocal laser scanning microscopy (CLSM) was performed to identify an intact layer of mesothelial cells (MC) underlying sites of ME attachment. Also, ME and MC were labelled with Cell-Tracker dyes. ME was cultured with mesothelial monolayers for 1 h (n = 10). Cultures were examined with differential interference contrast and CLSM. Optical sections were taken and a three-dimensional model was constructed.

RESULTS

In the peritoneal explants, ME adhered to intact mesothelium. There was no evidence of transmesothelial invasion. CLSM of sections of the explants demonstrated an intact monolayer of cytokeratin positive cells below the sites of ME implantation. Cytokeratin negative and positive ME cells adhered to mesothelial cells. Likewise, the ME attached to cultured mesothelium. Orthogonal sections and three-dimensional reconstruction confirmed an intact monolayer of mesothelium underlying ME attachment sites.

CONCLUSIONS

This study confirms that ME adheres rapidly to intact peritoneal mesothelium. Further studies are needed that characterize the mechanisms of ME adhesion to, and migration through, mesothelial cells.

The alpha(2)beta(1) and alpha(3)beta(1) integrins do not mediate attachment of endometrial cells to peritoneal mesothelium

OBJECTIVE

To evaluate the possible role of mesothelial alpha(2)beta(1) and alpha(3)beta(1) integrins in the attachment of endometrial stromal cells (ESCs) and endometrial epithelial cells (EECs).

DESIGN

In vitro study.

SETTING

University medical center.

PATIENT(S)

Women of reproductive age (n = 26).

MAIN OUTCOME MEASURE(S)

Mesothelial cells were grown on collagen IV. Endometrial stromal cells and EECs were plated on mesothelial cells for 1 hour. Before plating, mesothelial cells or endometrial cells were incubated with antibodies to alpha2, alpha3, and beta1 integrin subunits. The effect of these antibodies on ESC and EEC binding to collagen IV and collagen I was also examined. The expression of collagen I, collagen IV, fibronectin, and laminin by cultured ESCs and EECs was examined.

RESULT(S)

The anti-integrin antibodies had no effect on endometrial binding to mesothelium. The beta1 integrin antibody decreased binding of ESCs and EECs to the collagen matrices. In culture, ESCs and EECs expressed collagen I, collagen IV, fibronectin, and laminin to varying degrees.

CONCLUSION(S)

The initial adhesion of ESCs and EECs to mesothelium is not mediated by beta1 integrins. In contrast, ESC and EEC attachment to collagen IV and collagen I, which are present in the submesothelial extracellular matrix, is mediated by beta1 integrins.

Local cytokines in endometrial tissue: the role of interleukin-8 in the pathogenesis of endometriosis

Endometriosis, defined by the presence of viable endometrial tissue outside the uterine cavity, is among the most common gynecologic disorders affecting women of reproductive age. Endometriosis is associated with an inflammatory peritoneal environment, where multiple cytokines and growth factors are found at elevated levels. Interleukin-8 (IL-8) is a cytokine that induces chemotaxis of neutrophils and is a potent angiogenic agent. In addition, IL-8 was recently found to stimulate proliferation of various cells. We have observed that IL-8 is elevated in the peritoneal fluid of women with endometriosis and the levels correlate with the severity of the disease. We hypothesized that IL-8 may play a role in the growth and maintenance of ectopic endometrial tissue not only by chemoattracting and stimulating leukocytes to secrete growth factors and cytokines, but also by directly affecting endometrial cell proliferation. We found that IL-8 mRNA and protein levels in the endometrium were significantly higher during early proliferative and late secretory phases than during the mid-cycle. IL-8 receptors A and B are also expressed in the endometrium mostly localized in the stroma. Interestingly, IL-8 receptor expression is higher in the eutopic endometrium of women with endometriosis compared to the endometrium of women without endometriosis. Endometrial cells in culture proliferate significantly when treated with IL-8, which is inhibited by anti-IL-8 neutralizing antibody. More convincingly, IL-8 antisense oligonucleotide treatment decreases IL-8 production by endometrial cells as well as cell proliferation when compared to non-sense oligonucleotide treatment. The addition of IL-8 reverses the inhibitory effect of IL-8 antisense oligonucleotides on cell proliferation. These findings suggest that IL-8 may act as an autocrine growth factor in the endometrium. We have also studied the effect of endometrial cell adhesion on IL-8 expression and observed that IL-8 stimulates the adhesion of endometrial cells to fibronectin. Treatment of the cells with anti-IL-8 neutralizing antibody inhibited partially the cell adhesion. Thus, IL-8 may also be relevant for stimulating the attachment of endometrial implants in the pathogenesis of endometriosis. In addition, adherence of endometrial cells induced further IL-8 expression by an integrin-dependent mechanism. In summary, IL-8 may act as an autocrine growth factor in the endometrium and may also play a role in the pathogenesis of endometriosis by promoting the vicious circle of endometrial cell attachment, cell growth, and further secretion of this cytokine.

Mesothelial cell-associated hyaluronic acid promotes adhesion of endometrial cells to mesothelium

OBJECTIVE

To evaluate the role of hyaluronic acid in the attachment of endometrial cells to mesothelium.

DESIGN

In vitro study of adhesion of endometrial stromal and epithelial cells to mesothelial cells.

SETTING

University medical center.

PATIENT(S)

Reproductive-age women without endometriosis undergoing surgery for benign conditions.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The effect of hyaluronidase treatment of mesothelial cells or endometrial cells on adhesion of (51)Cr labeled endometrial stromal and epithelial cells to monolayers of mesothelium was evaluated. The expression of CD44, the hyaluronate receptor, was evaluated by western blot.

RESULT(S)

Hyaluronidase pretreatment of mesothelial cells decreased the binding of endometrial stromal and epithelial cells to mesothelium by 39% (P< .02) and 31% (P< .03), respectively. There was no effect on endometrial cell binding to mesothelial cells or to collagen IV when the endometrial cells were pretreated with hyaluronidase. CD44 expression by endometrial stromal and epithelial cells was demonstrated by western blot.

CONCLUSIONS

This study demonstrates that mesothelial cell-associated hyaluronic acid is involved in attachment of endometrial stromal and endometrial epithelial cells to the mesothelium. We hypothesize that binding of hyaluronic acid by endometrial cells is involved in the pathogenesis of the early endometriotic lesion.

Differential expression of integrin alpha v and beta 3 in serosal tissue of human intraperitoneal organs and adhesion

OBJECTIVE

To assess the expression of integrin alpha v and beta 3 in the serosal tissue of intraperitoneal organs and adhesions in persons with and without adhesions.

DESIGN

Prospective study.

SETTING

Academic research centers.

PATIENT(S)

Fifty-seven patients undergoing abdominal or pelvic surgery.

MAIN OUTCOME MEASURE(S)

Integrin alpha v and beta 3 messenger RNA (mRNA) expression was evaluated by quantitative reverse transcription polymerase chain reaction.

RESULT(S)

The serosal tissue of the parietal peritoneum, uterus, fallopian tubes, ovary, and the large and small bowel, as well as peritoneal adhesions, skin, fascia, subcutaneous tissue, and omentum, expresses integrin alpha v and beta 3 mRNA. The level of alpha v and beta 3 mRNA expression varied among these tissues; expression of the former substance was highest in uterine serosa and lowest in the skin and small bowel, and expression of the latter substance was highest in the fallopian tubes and skin and lowest in the uterine serosa. Parietal peritoneum and adhesions express equal levels of integrin alpha v; however, integrin beta 3 expression was >100-fold lower in adhesions than in peritoneum. The level of integrin beta 3 expression in omentum, small and large bowels, and subcutaneous tissue was 100-fold to 10,000-fold lower than in other tissues.

CONCLUSION(S)

Serosal tissue of peritoneal organs and adhesions express variable levels of integrin alpha v and beta 3 mRNA. On the basis of such variation and the knowledge that tissue injury alters local integrin expression, integrins may play a key role in adhesion development, particularly in tissue with higher integrin expression.

Short-term culture of peritoneum explants confirms attachment of endometrium to intact peritoneal mesothelium

OBJECTIVE

To evaluate the initial adhesion of endometrium to the peritoneum.

DESIGN

Descriptive study using light and confocal laser-scanning microscopy, immunohistochemistry, and transmission electron microscopy.

SETTING

University-based laboratory.

PATIENT(S)

Women without endometriosis undergoing surgery for benign conditions.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Explants of peritoneum (n = 20), prepared from four patients, were cultured for 1 hour with mechanically dispersed proliferative or secretory endometrium. Peritoneum was cultured with endometrium from the same patient. Specimens were fixed and serially sectioned for hematoxylin and eosin stain, immunohistochemistry using an anti-cytokeratin monoclonal antibody, and transmission electron microscopy.

RESULT(S)

In 17 of 20 explants, endometrium was adherent to intact mesothelium. There was no evidence of transmesothelial invasion at any sites of attachment. Although in most cases endometrium was adherent to mesothelium via endometrial stroma, there were many sites of endometrial epithelium-mesothelium attachment. Confocal laser scanning microscopy demonstrated an intact monolayer of cytokeratin-positive cells below the sites of endometrial implantation. Transmission electron microscopy demonstrated intact, viable, mesothelial cells below sites of attachment.

CONCLUSION(S)

This study demonstrates that endometrium rapidly adheres to intact peritoneal mesothelium. In addition, this study demonstrates that endometrial epithelial cells, as well as stroma, can attach to mesothelium. Further studies are needed that characterize the mechanism of endometrial-mesothelial cell adhesion.

Immunobiology of endometriosis

OBJECTIVE

To provide a review of the humoral and cellular immunology of endometriosis and to discuss the rationale for future approaches to diagnosis and treatment.

DESIGN

Literature survey.

RESULT(S)

Defective immunosurveillance in women who are destined to develop endometriosis may allow for the survival of ectopic endometrial tissue. The evidence includes endometrial cell resistance to apoptosis, perhaps through the secretion of proteins that interfere with implant recognition and/or FasL expression by stromal cells, inducing apoptosis of Fas-bearing immune cells. Although the immune response may be defective, aspects of it clearly are enhanced in endometriosis, as is seen by the generalized polyclonal B-cell autoimmune activation and secretion of immune proteins. Several cytokines, chemokines, and growth factors (including vascular growth factors) are increased in women with endometriosis.

CONCLUSION(S)

A complex network of locally produced cytokines modulate the growth and inflammatory behavior of ectopic endometrial implants. Proinflammatory proteins from endometriotic lesions and associated immune cells contribute to the enhanced inflammatory reaction associated with endometriosis that subserves the survival of these lesions instead of leading to their demise.

Expression of the alpha2beta1 and alpha3beta1 integrins at the surface of mesothelial cells: a potential attachment site of endometrial cells

OBJECTIVE

To localize alpha2beta1 and alpha3beta1 integrins in the cell membrane of peritoneal mesothelium in vivo and in vitro.

DESIGN

Descriptive study using confocal and two-photon laser-scanning microscopy.

SETTING

University-based laboratory.

PATIENT(S)

Women without endometriosis undergoing surgery for benign conditions.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Peritoneal biopsies (n = 9) and mesothelial monolayer cultures (n = 4) were incubated with antibodies to the alpha2 and alpha3 subunits and to the intact alpha2beta1 and alpha3beta1 integrins. Specimens were examined with laser-scanning microscopy.

RESULT(S)

The alpha2 and alpha3 subunits and the intact alpha2beta1 and alpha3beta1 integrins were identified at the base of the mesothelial cells (i.e., toward the basement membrane). There was also expression of the alpha2 and alpha3 subunits and the intact alpha2beta1 and alpha3beta1 integrins at the cell surface (i.e., toward the peritoneal cavity).

CONCLUSION(S)

The resolution of the confocal and two-photon laser-scanning microscope enabled localization of integrins in mesothelial cells. The presence of alpha2beta1 (collagen-laminin receptor) and alpha3beta1 integrins (collagen-laminin-fibronectin receptor) at the base of mesothelial cells suggests a role for these molecules in adhesion to the basement membrane. The presence of these molecules at the cell surface suggests a potential locus for cell adhesion in such processes as endometriosis and cancer metastasis.

Whole explants of peritoneum and endometrium: a novel model of the early endometriosis lesion

OBJECTIVE

To determine whether whole fragments of endometrium can adhere to peritoneum with intact mesothelium.

DESIGN

Tissue culture and immunohistochemical study.

SETTING

University medical center.

PATIENT(S)

Reproductive-age women undergoing surgery for benign conditions.

INTERVENTION(S)

Explants of human peritoneum from the anterior abdominal wall and the posterior surface of the uterus were cultured with whole fragments of mechanically dispersed endometrium.

MAIN OUTCOME MEASURE(S)

Adhesion of endometrial fragments to the surface of the peritoneum was evaluated. Adherent endometrium was identified with the use of the dissecting microscope and by the performance of serial sections of the peritoneum explants. Immunohistochemical staining of the mesothelium with antibodies to cytokeratin was used to ensure an intact layer of mesothelium beneath the endometrial implants. Transmission electron microscopy also was used to evaluate this adhesion process.

RESULT(S)

Endometrium was identified attached to the surface of the peritoneum. Most of the implants did not have identifiable mesothelium beneath them, but most had intact mesothelium running up to the point of attachment. Approximately 10% of the endometrial implants had intact mesothelium at the site of attachment. Endometrial stromal cells, and not epithelium, attached to the mesothelium.

CONCLUSION(S)

Endometrium can attach to the mesothelial surface of the peritoneum. Endometrial stromal cells are involved in this attachment. Invasion through the mesothelium seems to occur rapidly.